If he entered into a plea agreement that resulted in an adjudication of guilt or a with-hold of adjudication of guilt then he would not be able to expunge his record no matter what offense he was charged with. The fact that he was on probation makes it almost certain that such an agreement was entered into. If he has been adjudicated guilty he cannot seal his record.
I believe aggravated stalking is one of the charges that cannot be sealed or expunged in any case, barring exceptional circumstances and a judicial order.
It is state specific. In the State of Florida, you are unable to expunge an aggravated stalking, even if adjudication is withheld. If you are inquiring about another state, you should contact an attorney practicing in that state for advice.